An accessory drive belt for an engine is driven by the crankshaft and may be operatively connected by pulleys to an air pump, an air conditioning compressor, a water pump, a power steering pump, and an alternator for driving these devices. The pulley associated with the alternator is much smaller than the pulley associated with the crankshaft, so the alternator rotor rotates at a relatively high speed. Also, the alternator rotor has a relatively high inertia, which results in a high rotational momentum due to the high speed.
The speed profile of the crankshaft may vary significantly during engine cycles, particularly when the engine has a small number of active cylinders. Accordingly, due to the rotational momentum of the alternator rotor, significant positive or negative tension may occur in the belt between the crankshaft and the alternator as speed variations occur in the crankshaft. As a result of these tension variations in the belt, belt noise or belt chirp may occur. Other problems include vibration and reduced durability of the drive belt system.
Certain conditions within the vehicle exacerbate this problem. Also, continually checking for the certain conditions may unnecessarily increase the processing load of the control device.